The present invention is directed to an apparatus for implantation into a bone in a patient""s spine or pelvis, and is particularly directed to an apparatus that, when implanted, is resistant to toggling in the bone and to being pulled from the bone.
Bone screws are used in the medical field for a variety of purposes. Typical uses for bone screws, also referred as bone anchors, include treating a bone fracture, attaching a corrective device to parts of a fractured bone in an area adjacent to the fracture, and attaching a corrective device to a group of bones, such as vertebrae of a spinal column.
Most known bone screws use a conventional screw design, i.e. a solid shank, with one or more external thread convolutions. The solid shank and external threads of the conventional bone screws can cause the bone screws to displace an undesirably large amount of bone when implanted. It is also known to use a corkscrew-style helical spike as a tissue anchor. The known corkscrew-style tissue anchors, when implanted, displace less bone than the conventional bone screws, but are generally not able to withstand high tensile loads without structural failure. European Patent No. 0 374 088 A1 discloses a bone screw having a twin-corkscrew design. In this twin-corkscrew design, which is formed by drilling a passage up through a screw having a solid shank and then machining out the material between the two corkscrews, the junction of the corkscrews with the shank is unlikely to be capable of structurally withstanding high tensile loads and repetitive fatigue loads. This structural weakness in the design of the screw in the EP 0 374 088 document is further compounded by the corkscrews having a larger overall diameter than the head of the screw where torque is applied.
One of the more challenging applications of a bone screw is implantation of the screw into the cancellous bone of a patient""s spine or pelvis. For example, bone screws are frequently implanted into the cancellous bone of a patient""s lumbar vertebrae during a spinal fixation procedure to correct scoliosis. Once implanted, the bone screws are used to mount suitable spinal fixation instrumentation, such as clamps, rods, and plates. Unfortunately, many of the known bone screws, such as those described above, can be susceptible to toggling in the vertebral body and can also pull out of the vertebral body due to the substantial forces on the screws from human body movement and muscle memory. In order to achieve a high pull-out resistance, it is known to thread a bone screw all of the way through a vertebrae and place a nut on the opposite side. However, use of such a nut increases the complexity of the surgical procedure.
Hence, it is desirable to provide an apparatus for implantation into a bone in a patient""s spine or pelvis in a minimally invasive endoscopic procedure, wherein the apparatus provides a platform for connecting spinal fixation instrumentation and, when implanted, is highly resistant to toggling in the bone and to being pulled out of the bone despite the substantial forces on the apparatus from human body movement and muscle memory.
The present invention is an apparatus for implantation into a bone in a patient""s spine or pelvis. The apparatus, when implanted, is resistant to toggling in the bone and to being pulled from the bone. The apparatus comprises a platform having a first surface for facing a bone in a patient""s spine or pelvis. The platform includes structure for connection to a spinal fixation implant. The apparatus further comprises at least one helical spike for embedding into the bone upon rotation of the platform. The helical spike projects tangentially from the platform and extends around a longitudinal axis. The helical spike has a tip portion at a distal end which penetrates into the bone as the platform is rotated. The helical spike further has a connecting portion at a proximal end connected to the platform and an intermediate portion extending between the connecting portion and the tip portion.
In accordance with one embodiment of the present invention, the apparatus comprises a pair of helical spikes extending around the longitudinal axis. The proximal ends of the pair of helical spikes are spaced 180xc2x0 apart.
In accordance with another embodiment of the present invention, the apparatus comprises three helical spikes extending around the longitudinal axis. The proximal ends of the three helical spikes are spaced 120xc2x0 apart.
In accordance with yet another embodiment, the present invention is an apparatus comprising at least one anchor for implantation into a bone. The anchor, when implanted, is resistant to toggling in the bone and to being pulled from the bone. The apparatus further comprises a spinal fixation implant for extending between and connecting a plurality of bones. The anchor includes a platform having a first surface for facing the bone. The platform further has structure for connection with the spinal fixation implant. The anchor further includes at least two helical spikes for embedding into the bone upon rotation of the platform. The helical spikes are spaced apart and project tangentially from the first surface on the platform. The helical spikes extend around a longitudinal axis. Each of the helical spikes has a tip portion at a distal end which penetrates into the bone as the platform is rotated. Each of the helical spikes further has a connecting portion at a proximal end that is connected to the platform, and an intermediate portion extending between the connecting portion and the tip portion.
In accordance with still another embodiment of the present invention, the apparatus comprises a first anchor for implantation into a first bone and a second anchor for implantation into a second bone spaced from the first bone. Each of the first and second anchors extends co-linearly along the longitudinal axis. The spikes that project from the platform of the first anchor extend in a first direction. The spikes that project from the platform of the second anchor extend in a second direction opposite the first direction. The spinal fixation implant comprises a member extending along the longitudinal axis and interconnecting the first and second anchors.